FR2644526A1 - BRAKE EFFORT HYDRAULIC AMPLIFIER - Google Patents

Abstract

The invention proposes a hydraulic force amplifier, more particularly for a vehicle braking system, comprising an amplification piston 2 guided in a sealed manner and able to slide in the bore of a housing, this amplification piston delimiting, by one of its front ends, an amplification chamber 4 and bearing, in its initial position, against a stop 28 provided in the housing, this amplifier comprising a braking valve 7 comprising an actuating piston 5 which can move relative to the amplification piston under the action of a force exerted on the pedal and whose initial position is also defined by means of a stop 28 provided in the housing, communication being established between the amplification chamber 4 and the supply tank, and another communication being interrupted with an auxiliary pressure source 30, for the initial position of the pistons 2, 5, while, during a displacement of the piston d 'actuation 5 in the direction of actuation with respect to the amplifying piston 2, the communication offered to the pressurized fluid with the supply tank is interrupted, while that with the auxiliary pressure source 30 is established, characterized in that that the cross section of the passage 14 offered to the pressurized fluid to the supply tank is only partially open in the initial position of the pistons and in that the cross section of the communication passage 14 leading to the supply tank can be fully open when the actuating piston 5 moves relative to the boost piston 2 in the direction of brake release.

Description

The present invention relates to a hydraulic force amplifier, more

  particularly for vehicle braking system, comprising an amplification piston guided in a sealed manner and capable of

  slide in the bore of a shoemaker, this amplification piston delimits

  as long as, by one of its front ends, an amplification chamber and coming to bear, in its initial position, against a stop provided in the case, this amplifier comprising a brake valve comprising a

  actuating piston which can move relative to the amplifier piston

  cation under the action of a force exerted on the pedal and the initial position of which is also defined using a stop provided in the case, a

  communication being established between the amplification chamber and the reservoir

  see supply, and another communication being interrupted with an auxiliary pressure source, for the initial position of the pistons, while, during a displacement of the actuating piston in the actuating direction relative to the piston amplification, communication

  offered to pressurized fluid with the supply tank is inter-

  broken, while that with the auxiliary pressure source is established.

  A force amplifier of this type is described on pages 98 and 99 of the manual ATE Brake Handbook, Bartsch Publishing House, Munich, 1979. The

  brake valve of this effort amplifier is essentially made up of

  cased by a control slide which is tightly guided in a longitudinal bore of the amplification piston. Two transverse holes open into this longitudinal bore of the amplification piston. One of

  these transverse holes communicate with an auxiliary pressure source

  while the other communicates with a supply tank.

  In the initial position of the control slide (the brakes are not activated), the first hole is closed and the second is open, so that communication is offered to the pressurized fluid between the amplification chamber and the reservoir d 'food. We can then move the control slide by actuating the pedal, which first of all closes the hole leading to the supply tank, then opens the hole leading to the auxiliary pressure source. The pressurized fluid flows from this auxiliary pressure source into the amplification chamber and pushes the amplification piston towards the maltre-cylinder. A pusher resting on the amplification piston activates the brake master cylinder. When the brake is released, the first hole will close again, the second hole leading to the supply tank will open, so that the pressurized fluid can escape from the amplification chamber, and the amplification piston

  can return to its original position.

  This brake release action must take place quickly.

  This means that the effective cross-section of the fluid return hole must be of sufficient size. The faster the release action is performed, the larger the piercing. In addition, the manufacturer is required to ensure that the dead brake actuation stroke is as small as possible. The first phase of pedal operation only serves to close the fluid return hole. It is only after this phase is completed and the pressure connection is open that the effective application of the brakes takes place. The distance covered by the pedal in the first phase is called dead travel. In order to make the latter minimal, it is required that the cross section of the fluid return hole which is

  offered to pressurized fluid is as small as possible.

  This conflict between the aims has so far been decided in favor of the speed of relaxation. We made do with an important dead race. This is why the present invention - aims to arrange the brake force amplifier so that the dead travel is

  shortened, while maintaining the release speed.

  To this end, the invention relates to a hydrau-

  force plate of the aforementioned type, which is characterized in that the cross section of the passage offered to the pressurized fluid towards the supply tank is only partially opened in the initial position

  pistons and in that the cross section of the communication passage

  cation leading to the supply tank can be opened completely

  when moving the actuating piston relative to the piston

  amplification in the direction of release of the brakes.

  Since the fluid return hole is already closed to a large extent in the initial position of the pistons, only a small stroke is necessary to completely close this bore so that the pressure connection can therefore be opened . The dead race is very short. Furthermore, the control slide can be moved relative to the amplification piston in the release direction when the brakes are released, so that the fluid return passage is completely open. As a result, the release speed

remains the same.

  In a particularly simple manner, the present invention can be implemented with a force amplifier, the brake valve of which comprises a control slide. For this purpose, in its initial position, this control drawer must simply be placed so as to close to a significant extent the transverse bore of the passage of

fluid return.

  The present invention can however also be used on effort amplifiers comprising seat valves, as is

  described for example in published German patent application 2,909,685.

  The stops provided for the pistons must only be arranged in such a way that the valve closing element acting on the fluid return hole is arranged directly in front of the valve seat. Another field of application is that of hydraulic force amplifiers in which the brake valve is not placed inside the amplification piston, but is guided in a particular bore of the boltier and is actuated with the using a lever mechanism, the lever arms attacking on the one hand the actuating piston and on the other hand the amplification piston. We will refer to the German patent application

published 3,507,488.

  In order to allow that existing effort amplifiers can be easily adapted if necessary and / or that an existing production line can be used, it is proposed to place on the actuating piston a sleeve which is disposed between a circumferential collar provided on the actuating piston and the stop integral with the housing. This allows the actuating piston and therefore the control slide to be returned to their initial position only

  to such an extent that the fluid return hole is not completely

openly,

  Other characteristics and advantages of the invention stand out

  will derive from the description which follows, given by way of non-limiting example

  and opposite the appended drawing in which the single figure represents a particular embodiment of a hydraulic force amplifier

according to the invention.

  This hydraulic force amplifier consists of a boot 1 in which an amplification piston 2 is guided in a way

  waterproof. The amplification chamber 4 is provided between this amplification piston.

  cation 2 and the rear wall 3 of the housing 1 of the amplifier. An actuating piston 5 tightly crosses the rear wall 3. A rod

  pedal 6, which is coupled to the pedal mechanism shown diagrammatically

  Only attack the actuating piston 5 from the outside. The valve

  braking 7 essentially consists of a control drawer 8 comprising

  as a longitudinal bore 9. This control slide 8 is guided in a bore 10 of the amplification piston 2 or of an intermediate piece 11 mounted in this amplification piston; It is in this bore 10 that a pressure bore 12 opens which is connected to an annular groove 12 'formed on the inner face of the bore 10. This pressure bore 12 leads to an annular chamber 13, located on the surface peripheral of

  amplification piston 2, which communicates with an auxiliary pressure source

  liaire 30 via a housing connector.

  Furthermore, a fluid return hole 14 with a diameter of about 1.7 mm opens into the bore 10 and communicates with a chamber which is not under pressure and is arranged on the side of the amplification piston. 2 which is located opposite the amplification chamber 4. This pressureless chamber 15 communicates permanently with a supply tank 31 by means of a connection hole made in the housing 1. On the side adjacent to the pressure-free chamber 15, the bore 10 is closed off by a closing piece 16. It is on this

  closing part 16 supported by a pusher 17 which transmits the movement

  amplification piston 2 to the master cylinder piston. Room

  18 is provided between the closing part 16 and the control drawer 8.

  The longitudinal bore 9 of this control drawer opens into this chamber. This longitudinal bore 9 provides the pressurized fluid with a

  permanent communication with the amplification chamber 4 via

  diary of a first transverse hole 16. A second transverse hole

  , which can also be called control drilling, communicates the

  longitudinal sage 9 with a control groove 20 'located on the outer face

control drawer 8.

  The control slide 8 itself is rigidly connected to the actuating piston using a latching means. At the end of the drawer which is close to the actuating piston 5, its outer face has a

  protruding circlip 22 which can snap behind a circumferential rim

  rentiel 23 provided on the actuating piston 5.

  The amplification piston 2 has a sleeve-shaped extension 24 which projects into the amplification chamber 2. An annular ring 25 serving as a stop is fitted into the interior face of this sleeve 24. At its end extending in the amplification chamber 2, the outer face of the actuating piston 5 has a flange

circumferential 26.

  It is on this circumferential collar 26 provided on the

  actuating piston 5 directly supported by a socket 27 comprising

  both a flange 29 oriented radially outwards. This socket

  thus offers an L-shaped profile when viewed in cross section.

  The base part of this socket is arranged between the glue-

  circumferential rette 26 and a stop 28 provided on the rear wall 3, while the flange 29 is placed between the annular ring 25 and this stop 28. When it is supported on this stop 28, the sleeve thus defines the initial position provided for the actuating piston 5 of a

  on the one hand and for the amplification piston 2 on the other.

  A spring 32, which is interposed between the intermediate piece 11 and a part forming a pendant which is disposed on the control drawer 8, defines the initial position of this control drawer 8 relative to the

amplification piston 2.

  The effort amplifier works in accordance with the following principle: The figure shows the initial position of the effort amplifier. The grooves 12 'and 20' do not overlap. The drawer of

  control 8 blocks most of the fluid return bore 14.

  Only a small cross section or segment of circular shape remains, the area of which is considerably smaller than the area of any

  the circular section of the fluid return hole. The cross-section

  remaining soil is sufficient to create a pressure balance in the event that the fluid present in the amplification chamber expands or becomes

  compresses, for example under the effect of temperature.

  To apply the brakes, the pedal is operated and, so that the actuating piston and therefore the control slide are moved in the actuating direction (to the left in the representation

  of the figure). The fluid return hole 14 is already complete.

  closed after a short run. A small additional displacement causes the grooves 12 ′ and 20 ′ to overlap, so that, from the auxiliary pressure source 30, the pressurized fluid reaches the amplification chamber 4 passing through the annular chamber 13, the hole 12, the control hole 20 of the longitudinal bore 9 and the

transverse drilling 19.

  The pressurized fluid pushes the amplification piston in the direction of actuation, so that the part on which the plunger 17 acts, for example a brake master cylinder, is actuated. In this regard, the amplification piston 2 is in advance, in its movement, relative to the control slide 9 and the grooves 12 'and 20' leave their overlapping position, so that further actuation cannot take place only if the actuating piston 5 continues to be moved under the action of the force exerted by the pedal. When the brake is actuated, the actuating piston 5 and the amplification piston 2 both leave their abutment in abutment on the sleeve 27. They can then move freely, one relative to the 'other. If the driver then releases the pedal during braking, the actuating piston 5 and therefore the control slide 9 are no longer subjected to the action of a force. The pressure prevailing in the amplification chamber 4, as well as the force exerted by the spring 29, elastically push the control slide relative to the amplification piston 2 in the direction of release of the brake. In doing so, the control slide 9 moves back, sliding, to such an extent that the cross section of the fluid return bore 14 is completely open. The pressurized fluid present in the amplification chamber 4 can escape, without being the subject of a constriction, through this cross section of a sufficient size, so that the amplification piston 4 is brought back quickly in its initial position under the action of a return spring not shown. A cross section of the fluid return hole 14 which is too small in size would prevent the pressurized fluid from returning from the amplification chamber 4 to the supply tank 31 and would greatly reduce the return speed to the initial position.

  -In principle, the intermediate part 27, which has a cross-section

  L-shaped versal, can also be designed as part of case 1.

  However, a separate intermediate piece makes it possible to adapt existing brake force amplifiers and / or it is possible to adopt an existing production process for such an amplifier,

  since it is only necessary to add a production step

  tion during which the sleeve 27 is threaded on the action piston-

5.

Claims (8)

  1. Hydraulic force amplifier, more particularly for vehicle braking system, comprising an amplification piston (2) guided in leaktight manner and capable of sliding in the bore of a shoemaker, this dramplification piston delimiting, by one of its front ends, an amplification chamber (4) and coming to bear, in its   initial position, against a mound (28) provided in the case, this amplifier   ficitor comprising a brake valve (7) comprising a piston   actuator (5) which can move relative to the amplifier piston   cation under the action of a force exerted on the pedal and the initial position of which is also defined using a stop (28) provided in the case, a communication being established between the amplification chamber   (4) and the supply tank, and another communication being inter-   broken with an auxiliary pressure source (30), for the initial position of the pistons (2, 5), while, during a displacement of the actuating piston (5) in the actuating direction relative to the piston d amplification (2), the communication offered to the pressurized fluid with the supply tank is interrupted, while that with the auxiliary pressure source (30) is established, characterized in that the cross-section   transverse passage (14) offered to pressurized fluid to the reservoir   see feed is only partially opened in the initial position   the pistons and in that the cross section of the commu-   indication (14) leading to the supply tank can be opened completely when the actuating piston (5) is moved relative to   to the amplification piston (2) in the direction of release of the brakes.   2. Braking system according to claim 1, characterized in that the brake valve (7) comprises a control slide (8) which   is coupled to the actuating piston (5).   3. Braking system according to claim 2, characterized in that an edge of the control slide, located opposite the pedal, overlaps a transverse bore (14) formed in the amplification piston (2), the most of this transverse hole (14) being covered in the initial position of the pistons (2, 5), while this same transverse hole (14) is completely closed when the drawer is actuated   control in the direction of actuation.   4. Braking system according to claim 1, characterized in that at its front end contiguous to the amplification chamber (4), the amplification piston has a sleeve-shaped extension (24), an annular ring ( 25) being fitted onto the inner edge of this extension. 5. Braking system according to claim 3, characterized in that at its end which projects into the amplification chamber (4), the actuating piston (5) comprises a circumferential collar (26) on its outer edge.   6. Braking system according to claim 5, characterized in that a socket (27) is disposed between the flange   circumferential (26) and the mound (28) integral with the housing.   7. Braking system according to one of claims 4, 5 and   6, characterized in that the sleeve (27) has a radial extension (29), so that this sleeve (27) has an L-shape in cross section and in that this radial extension (29) projects into the space between the annular ring (25) and the stop (28) integral with the housing.   8. Braking system according to any one of   previous claims, characterized in that the return drilling of   fluid (14) has a diameter of about 1.7 mm.